The present invention relates to a method for producing a leadthrough for an optical conductor in a housing part.
Corresponding leadthroughs are known for example from EP 0 267 536. These are used for hermetically sealed housings of electro-optical or optoelectronic components in order to protect these from external environmental influences, e.g. dust or moisture.
An embodiment of the state of the art is presented in FIGS. 2a-2d. FIG. 2a shows a top view of a housing with a corresponding leadthrough. FIG. 2b is a sectional view along the line A-A in FIG. 2a. The housing consists of two parts 1,7. The leadthrough for a glass fibre 3 is arranged in one part 1. The housing part 1 has a stepped hole into which the glass fibre has been introduced. For sealing off, the glass fibre is glued in the stepped hole with an adhesive 4. Optionally, a protective hose 5 can be used which is glued into the hole and into which the glass fibre is glued.
The leadthrough must be hermetically sealed overall. As the customarily used adhesives, such as e.g. epoxy adhesives, display a degree of permeability to air and water vapour, the hole must be correspondingly long and have as small as possible a cross-section so that, when glued, the result is as long as possible a diffusion length with as small as possible a diffusion cross-section for the adhesive. In particular, the requirement of the long diffusion length means that the housing part 1 must have a thickness which corresponds at least to the diffusion length. As a rule, therefore, merely because of the necessary diffusion length the housing part must be thicker than is necessary on mechanical grounds, which leads to increased material costs and above all a greater space requirement for the component.
As a rule, the housing parts are made by means of methods for cutting from the solid.
In principle, it is desired to produce the housing part in a simpler and above all cheaper way. Production by the injection moulding process is not possible, however, as holes with an aspect ratio greater than 5 cannot be produced with the necessary accuracy for the required small cross-sections by the injection moulding process.
It is also known to produce housing parts by means of powdered metal injection moulding. In powdered metal injection moulding, firstly an injectable granular material comprising powdered metal and binders, usually organic binders, such as e.g. a combination of waxes and plastics, is mixed in a precisely defined proportion by volume.
The resultant injectable granular material can then be converted into a shaped body with the help of the injection moulding process.
The injection moulding can be carried out on conventional injection moulding machines, such as are known for example from plastics processing. It is to be borne in mind that, because of the high proportion by volume of plastic and depending on the binder used and the powdered metal, the thus-produced green bodies are approx. 15 to 20% larger than the product to be produced. The green body nevertheless has all the typical geometric features of the finished component.
Generally, in the next step a large part of the organic binder which gave the powdered metal its injectable properties is removed again from the green body. The residual binder content is reduced by the so-called debindering process to approx. 2 to 3%, which guarantees that the shaped body still has a degree of stability.
In the last step the components are sintered at temperatures a little below their melting point (usually between 1200° C. and 1400° C.) and there obtain their ultimate size. The thus-finished metallic part can in principle have all geometric shapes that can be produced by means of injection moulding.
However, even with this method it is basically not possible to produce passage openings with the required small cross-sections and an aspect ratio of more than 5 which are, however, necessary for a hermetically sealing glass fibre leadthrough.
Starting from the described state of the art it is therefore the object of the present invention to provide a method for producing a leadthrough for an optical conductor in a housing which is cost-favourable and also allows the necessary dimensions of the housing part to be minimized.